1. Field of the Invention
Embodiments disclosed herein relate generally to wellbore fluids. In particular embodiments disclosed herein relate to reclamation of brines in wellbore fluids.
2. Background Art
In the oil recovery industry and in hydrocarbon recovery, drilling fluids and well servicing fluids are used on a regular basis. When drilling or completing wells in earth formations, various fluids typically are used in the well for a variety of reasons. Common uses for well fluids include: lubrication and cooling of drill bit cutting surfaces while drilling generally or drilling-in (i.e., drilling in a targeted petroliferous formation), transportation of “cuttings” (pieces of formation dislodged by the cutting action of the teeth on a drill bit) to the surface, controlling formation fluid pressure to prevent blowouts, maintaining well stability, suspending solids in the well, minimizing fluid loss into and stabilizing the formation through which the well is being drilled, fracturing the formation in the vicinity of the well, displacing the fluid within the well with another fluid, cleaning the well, testing the well, transmitting hydraulic horsepower to the drill bit, emplacing a packer, abandoning the well or preparing the well for abandonment, and otherwise treating the well or the formation.
The drilling fluids and other well servicing fluids that are used are either lost during the completion or drilling operation or recovery operation or, if recovered, are typically discarded. However, with increasing technology, the completion or drilling fluids either for an environmental reason and/or expense reasons are being recovered for reuse. This is especially true with high tech well servicing and drilling fluids that are quite expensive, and thus their recovery is relatively important since being able to use the well servicing fluids, and in particular the brine in the well servicing fluids, will greatly reduce the cost of future completion or drilling operations.
Brines (such as, for example, aqueous CaBr2) commonly are used as well fluids because of their wide density range and the fact that brines are typically substantially free of suspended solids. In addition, brines are often used in order to achieve a suitable density for use in well completion or drilling operations. Typically, brines comprise halide salts of mono- or divalent cations, such as sodium, potassium, calcium, and zinc. Chloride-based brines of this type have been used in the petroleum industry for over 50 years; bromide-based brines, for at least 25 years; and formate-based brines, for roughly the past ten years. One additional advantage of using brines is that brines typically do not damage certain types of downhole formations; and for formations that are found to interact adversely with one type of brine, often there is another type of brine available with which those formations will not interact adversely.
A variety of compounds are typically added to brine-based well fluids. For example, a brine-based well fluid may also include viscosifiers, corrosion inhibitors, lubricants, pH control additives, surfactants, solvents, and/or weighting agents, among other additives. Some typical corrosion inhibitors include amine-based or inorganic thiocyanate-based compounds, which are designed to help prevent general corrosion attack on casing, tubing and downhole tools in contact with the completion or drilling fluid.
While thiocyanates are useful inhibitors at some low to medium temperature ranges, at temperatures of 350° F. (177° C.) and upwards, thiocyanates and other sulfur-containing additives are believed to be prone to thermal decomposition and subsequent environmentally induced corrosion cracking of tubular goods, especially those of high strength corrosion resistant alloys. However, sulfates are not believed to be among this group of sulfur containing additives believed to be prone to thermal decomposition and subsequent environmentally induced corrosion cracking of tubular goods. Stress corrosion cracking has also been postulated to be a risk as a result of hydrogen sulfide production from the decomposition of thiocyanates.
In the life cycle of completion brine, initially formulated stock brines are custom-blended with a variety of additives depending on the particular application. If the list of additives includes corrosion inhibitors, then the brine may have come to contain thiocyanates by deliberate addition; however, cross-contamination may also be a reason for a used completion brine to contain thiocyanates. Once used, a completion fluid that is returned to the surface may optionally be subjected to reclamation processes for reuse in a subsequent application. Such fluids may be contaminated with any or all of the following: water, drilling mud, formation materials, rust, scale, pipe dope, and viscosifiers and bridging agents used for fluid-loss-control pills. Depending on their composition and level of contamination, these fluids may or may not have further practical or economic value. If it is deemed that the fluids have future use potential, they may be reclaimed. Conversely, if they are determined to have no further use, they must be disposed of in an environmentally responsible way.
Conversely, if it is deemed that the fluids have future use potential, they may be reclaimed. There are many known methods for removing contaminates from a brine solution. Among the various approaches removal of suspended solids by filtration, pH adjustments, chemical treatment, carbon treatment, etc. Current API recommended practices specify the testing for such components such as solids, pH, and iron; however, it is likely that in the future the recommended practices will also include a specification on the maximum allowable thiocyanate content. Furthermore, while a thiocyanate-based additive may be innocuous in a first, medium temperature drilling operation, a subsequent drilling operation may be at higher temperatures, presenting a risk of thiocyanate degradation and hydrogen sulfide production. Reclamation processes to date have not focused on the removal of thiocyanates from brines.
Accordingly, there exists a need for reclamation processes for brines in which thiocyanates may be effectively removed therefrom for reuse in subsequent operations.